Critics Sharpening Attacks on Halperin, Controversial Nominee for Defense Post : Pentagon: GOP links ex-NSC staffer to leaking classified papers, abetting ex-CIA agent Agee. His bid to return to government has created a new furor.

WASHINGTON — The last time Morton H. Halperin had a sensitive government job, he left with a bang.

He quit his job on the National Security Council staff to protest the 1970 U.S. invasion of Cambodia, then sued his boss--Henry A. Kissinger--for wiretapping his home to learn whether he had leaked documents about secret American bombing in the country.

He spent the next 23 years criticizing the Vietnam War, advocating deep cuts in nuclear weapons and opposing covert military operations abroad--first on the staffs of liberal think tanks and later as head of the Washington office of the American Civil Liberties Union.

Now the 55-year-old civil libertarian and defense expert has sparked a new furor with what some see as his most unlikely move of all--a bid to return to government, this time to the Pentagon, the agency that has most resented his activities.

Republicans on the Senate Armed Services Committee, spurred by the Center for Security Policy, a conservative advocacy group, are trying to block Halperin's nomination as an assistant secretary of defense responsible for military peacekeeping operations.

So far the efforts have proved effective. Ten months after the Clinton Administration took office, Halperin's nomination--quietly sent to Congress last summer--still is hanging in the balance.

Armed Services is almost evenly split over the appointment and has yet to schedule a hearing on it. And recent reports have suggested that the White House has been carefully reviewing Halperin's writings and record.

With the White House conspicuously silent on the nomination, some supporters fear that Halperin may now be heading for the same fate as C. Lani Guinier, the civil rights lawyer whose contested nomination to head the civil rights division in the Justice Department eventually was withdrawn.

"Whether he (Halperin) gets a hearing will depend critically on whether the Administration wants to press for one," says Arnold Kanter, a former George Bush Administration official with the National Security Council and State Department, and a supporter of Halperin.

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Even if Halperin does win a hearing soon, strategists say that his prospects are uncertain. Republicans have threatened a filibuster if the appointment ever reaches the Senate floor. And the White House does not yet have the votes to block it.

By all indications, the Administration clearly has been taken aback by the intensity of the opposition.

When Halperin's name first was suggested by Defense Secretary Les Aspin, who tailor-made the new post for him, insiders expected some grumbling from Congress. But most were confident that Aspin--himself a former lawmaker--would be able to push the nomination through.

But the campaign by Halperin's opponents has been fierce, even by Washington standards.

Republicans charge that Halperin "was implicated in" leaking classified documents in the Pentagon Papers case of the early 1970s; "abetted" former CIA agent Philip Agee in revealing the identities of U.S. spies, and "is widely distrusted" by national security experts.

Sen. Strom Thurmond (R-S.C.) wrote colleagues on the Armed Services Committee that Halperin has a long history of "extreme and irresponsible" positions on key national security issues that raise serious questions about his judgment and reliability.

He also branded Halperin "a master of duplicity and pretense."

And Frank J. Gaffney Jr., director of the Center for Security Policy, has launched a one-man crusade against Halperin's nomination, calling on Clinton to withdraw it soon to "spare your Administration unnecessary anguish and political costs."

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At first blush, many of Halperin's crusades seem tame by today's standards: he opposed wiretapping and covert operations by U.S. intelligence agencies, both at home and abroad. And he has argued that the government classifies too many documents.

But others of his causes were dynamite during the Cold War--some so much so that even he has abandoned them. The nominee argued during the 1980s that the Soviet posture in Europe was "defensive and deterrent." And he once opposed clandestine intelligence-gathering.

What really rankles conservatives, however, is Halperin's association with two men whom national security officials regard as villains--Agee, and Daniel Ellsberg, the man who leaked the Pentagon papers, which revealed secrets on how Washington got mired in the Vietnam War.

Critics also blanche at his having publicly defended Ronald L. Humphrey and David Truong, who were convicted during the late 1970s of having stolen classified documents and funneling them to the North Vietnamese. Halperin argued that the materials never should have been classified.

Many Republicans and Democrats who have served in national security posts and are familiar with Halperin's record contend that the conservatives' charges are overblown--and, in some cases, riddled with inaccuracies.